Obesity and type 2 diabetes, hypertension, and cardiovascular disease, are diseases that feature serious disturbances in glucose or lipid metabolism that severely affect the health and quality of life of affected individuals. In addition, cancer metabolism is known to be difference from normal cellular metabolism. The increasing prevalence of these diseases makes finding new drug targets for treating these syndromes an urgent task.
AMP-activated protein kinase (AMPK) acts as a cellular energy sensor and regulator. It is activated by an increase in the cellular AMP:ATP ratio induced by metabolic stress, hormone and nutrient signals, and other cellular mechanisms such as phosphorylation and protein-protein interaction. Once activated, AMPK switches on catabolic pathways that generate ATP and switches off ATP-consuming anabolic pathways by acute regulation of the activity of key enzymes in metabolism and chronic regulation of the expression of pivotal transcription factors (Hardie, D G. Nature reviews 8 (2007b), 774-785; Woods, A et al. Molecular and cellular biology 20 (2000), 6704-6711). The growing evidence of AMPK regulatory effects on glucose and lipid metabolism makes it a potential drug target for treatment of diabetes, metabolic syndrome and cancer (Carling, D. Trends Biochem Sci 29 (2004), 18-24; Hardie, D G. Annual review of pharmacology and toxicology 47 (2007a), 185-210; Kahn, BB et al. Cell metabolism 1 (2005), 15-25; Long, Y C et al. The Journal of clinical investigation 116 (2006), 1776-1783).
At the physiological level, this concept has been supported by two adipokines, leptin and adiponectin, both of which exert excellent effects on glucose and lipid metabolism (Friedman, J M and Halaas, J L. Nature 395 (1998), 763-770; Muoio, D M et al. Diabetes 46 (1997), 1360-1363; Yamauchi, T et al. Nature medicine 7 (2001), 941-946). Recent studies suggest that leptin and adiponectin exert their antidiabetic effects by activating AMPK. Leptin stimulates muscle fatty acid oxidation by activating AMPK directly and through a hypothalamic-adrenergic pathway (Minokoshi, Y et al. Nature 415 (2002), 339-343). Adiponectin stimulates glucose uptake and fatty acid oxidation in vitro by activation of AMPK. Furthermore, it exerts its hypoglycemic effect by decreasing PEPCK and G6Pase expression, whereas the administration of dominant negative α1 adenovirus reverses the effect in vivo (Yamauchi, T et al. Nature medicine 8 (2002), 1288-1295).
At the pharmacological level, the concept of AMPK as a potential target for treating metabolic syndrome has been further supported by the discovery of two major classes of existing antidiabetic drugs: thiazolidinediones (rosiglitazone, troglitazone and pioglitazone) and biguanides (metformin and phenformin) activate AMPK in cultured cells and in vivo. Rosiglitazone is traditionally considered to be a PPARγ agonist and exerts its antidiabetic effects through differentiation of adipocytes (Semple, R K et al. The Journal of clinical investigation 116 (2006), 581-589). Recent findings indicate that AMPK may be involved in the antidiabetic effects of rosiglitazone (Brunmair, B et al. The Journal of biological chemistry 277 (2002), 25226-25232; Kadowaki, T et al. The Journal of clinical investigation 116 (2006), 1784-1792). In the case of metformin, an existing antidiabetic agent without a defined mechanism of action, recent studies demonstrate that it could activate AMPK in vitro and in vivo by inhibiting complex I (El-Mir, M Y et al. The Journal of biological chemistry 275 (2000), 223-228; Owen, M R et al. The Biochemical journal 348 Pt 3 (2000), 607-614; Zhou, G et al. The Journal of clinical investigation 108 (2001), 1167-1174), and the hypoglycemic effect could be blocked completely by knockout of its upstream kinase LKB1, confirming the key role of AMPK in mediating the antidiabetic effect of metformin (Shaw, R J et al. Science (New York) N.Y. 310 (2005), 1642-1646).
Most recently, Cool and coworkers have identified a small direct AMPK activator, A-769662, which exerts antidiabetic effects in vivo (Cool, B et al. Cell metabolism 3 (2006), 403-416). Li's laboratory has also identified a small AMPK activator, PT1, which activates the inactive forms of AMPK α2398 and α1394 with micromolar activity and exerts some cellular effects (Pang, T et al. The Journal of biological chemistry 283 (2008), 16051-16060).